Date: Wed, 25 Nov 2015 14:32:53 -0600
From: Rob Herring <robh@kernel.org>
To: Damien Riegel <damien.riegel@savoirfairelinux.com>
Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-watchdog@vger.kernel.org, devicetree@vger.kernel.org,
        Lee Jones <lee.jones@linaro.org>, Pawel Moll <pawel.moll@arm.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Ian Campbell <ijc+devicetree@hellion.org.uk>,
        Kumar Gala <galak@codeaurora.org>,
        Russell King <linux@arm.linux.org.uk>, Shawn Guo <shawnguo@kernel.org>,
        Sascha Hauer <kernel@pengutronix.de>, Arnd Bergmann <arnd@arndb.de>,
        Samuel Ortiz <sameo@linux.intel.com>, Wim Van Sebroeck <wim@iguana.be>,
        Guenter Roeck <linux@roeck-us.net>, kernel@savoirfairelinux.com
Subject: Re: [PATCH v6 2/6] mfd: syscon: add a DT property to set value width
Message-ID: <20151125203253.GA13437@rob-hp-laptop>
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On Wed, Nov 25, 2015 at 02:25:03PM -0500, Damien Riegel wrote:
> Currently syscon has a fixed configuration of 32 bits for register and
> values widths. In some cases, it would be desirable to be able to
> customize the value width.
> 
> For example, certain boards (like the ones manufactured by Technologic
> Systems) have a FPGA that is memory-mapped, but its registers are only
> 16-bit wide.
> 
> This patch adds an optional "bus-width" DT binding for syscon that
> allows to change the width for the data bus (i.e. val_bits). If this
> property is provided, it will also adjust the register stride to
> bus-width / 8. If not provided, the default configuration is used.

See the 8250 UART bindings. This problem is already solved and has 
standard bindings for it.

Rob

> 
> Signed-off-by: Damien Riegel <damien.riegel@savoirfairelinux.com>
> Acked-by: Arnd Bergmann <arnd@arndb.de>
> Acked-by: Lee Jones <lee.jones@linaro.org>
> ---
>  Documentation/devicetree/bindings/mfd/syscon.txt |  3 +++
>  drivers/mfd/syscon.c                             | 13 +++++++++++++
>  2 files changed, 16 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/mfd/syscon.txt b/Documentation/devicetree/bindings/mfd/syscon.txt
> index fe8150b..4c9d187 100644
> --- a/Documentation/devicetree/bindings/mfd/syscon.txt
> +++ b/Documentation/devicetree/bindings/mfd/syscon.txt
> @@ -13,6 +13,9 @@ Required properties:
>  - compatible: Should contain "syscon".
>  - reg: the register region can be accessed from syscon
>  
> +Optional property:
> +- bus-width: width of the data bus. Can be <8>, <16>, <32>, or <64>.
> +
>  Examples:
>  gpr: iomuxc-gpr@020e0000 {
>  	compatible = "fsl,imx6q-iomuxc-gpr", "syscon";
> diff --git a/drivers/mfd/syscon.c b/drivers/mfd/syscon.c
> index 176bf0f..5a93d80 100644
> --- a/drivers/mfd/syscon.c
> +++ b/drivers/mfd/syscon.c
> @@ -47,6 +47,7 @@ static struct syscon *of_syscon_register(struct device_node *np)
>  	struct syscon *syscon;
>  	struct regmap *regmap;
>  	void __iomem *base;
> +	u32 bus_width;
>  	int ret;
>  	struct regmap_config syscon_config = syscon_regmap_config;
>  
> @@ -69,6 +70,18 @@ static struct syscon *of_syscon_register(struct device_node *np)
>  	 else if (of_property_read_bool(np, "little-endian"))
>  		syscon_config.val_format_endian = REGMAP_ENDIAN_LITTLE;
>  
> +	/*
> +	 * search for bus-width property in DT. If it is not provided, default
> +	 * to 32-bit. regmap_init_mmio will return an error if syscon_config's
> +	 * values are invalid so there is no need to check them here.
> +	 */
> +	ret = of_property_read_u32(np, "bus-width", &bus_width);
> +	if (ret)
> +		bus_width = 32;
> +
> +	syscon_config.val_bits = bus_width;
> +	syscon_config.reg_stride = syscon_config.val_bits / 8;
> +
>  	regmap = regmap_init_mmio(NULL, base, &syscon_config);
>  	if (IS_ERR(regmap)) {
>  		pr_err("regmap init failed\n");
> -- 
> 2.5.0
> 
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